Technological improvements in industry require accurate control of the flow of high-pressure fluids or gasses. Gate valves are typically used where the flow of fluid or gas is seldom interrupted, so that the quantity of flow is the main consideration. Gate valves allow maximum flow while exercising control through the closure of a sliding gate transverse to the flow. The gate is user controlled either through a spindle screw or other means so as to allow adjustments in flow rate. The primary advantage of a gate valve is that the original flow rate of the fluid or gas is not impaired by installing the valve body.
Various types of gate valve assemblies are known for opening and closing pipelines to control the flow of fluid or gas. The traditional gate valve body provided a single metallic disk capable of stopping the flow of a liquid or gas through an inlet port and out through an outlet port by movement of the gate valve into a closed position transverse to flow from the inlet port. The single disk is typically mounted with a little play such that the uneven pressure on one side of the disk from the inlet side acts to deform the gate or the seat into which it slides when in a closed position. This deformation can allow leakage, and force repair or replacement. Alternatively, the use of a single metal disk to seal off flow can be hindered due to rubbing of the disk against the seating surfaces of the valve body, and in this way, slowly damages the single disk or seating surface such that the gate valve body does not adequately restrict flow and prevent leakage.
U.S. Pat. No. 4,483,514, "GATE VALVE MEMBER FOR RESILIENT-SEATED GATE VALVE", by the inventor of the present invention, shows a prior-art gate valve.
One attempt to efficiently prevent leakage or deformation is a gate valve assembly having two disks. The disks are disposed between two opposite seat surfaces, each facing either an inlet port or an outlet port. When actuated, the double disk construction sealingly engages the respective seat surface as the gate assembly moves into a closed position. The disks may be pressed outwards against the seats by a spring assembly, or by fluid pressure introduced between the disks.
U.S. Pat. No. 4,913,400, "DOUBLE DISK GATE VALVE", issued in 1990 to Tiefenthaler, shows a prior art double-disk gate valve which is biased outward by fluid pressure.
Gate valve assemblies employing double disk closure gates are further improved through the incorporation of resilient sealing material around the periphery of the disks themselves. When the gate assembly is put into a closed position, the resilient materials located on the peripheral surfaces of the gate are deformed through the application of pressure, thereby helping to provide a tighter seal between the seat surfaces and the gate assembly than accomplished by bare disks of the gate assembly.
However, these configurations employing resilient sealing members around the periphery of a seat ring must be constructed to within narrow tolerances to insure appropriate sealing characteristics. The tolerances must be even more precise when the side wall portions of the seat surface as formed by the seat recess sidewall are considered. The prior art typically mounts these resilient members on the periphery of the gate assembly, making the dimensional tolerances of the resilient member very narrow, to prevent compression of the resilient member beyond its elastic limit. This maintenance of narrow tolerances for resilient sealing members requires significant manufacturing oversight, is time-consuming, and is an expensive factor limiting the application of double disk gate valves.
In addition, the prior art teaches the construction of the double disk valve assembly essentially of metal. This construction is expensive and makes the valve body installed very heavy.